Thursday, January 29, 2009

NFL Wrapup: APR Pick Reliability

Over the course of the regular season, APR picked 240 NFL games
week 2 to week 17. I am counting the Bengals @ Eagles tie
game as a push in the following tallies.

Visitor vs Home:

VisitorWon

HomeWon

Total

Picked Right

69

90

159

Picked Wrong

34

46

80

Total

103

136

239

APR picked the home team to win 124 times (90 right + 34 wrong).
Since 136 home teams won, that's pretty good evidence that some kind of
factor should be added to favor home teams in generating picks.

Picks by Matchup Ratio

The matchup ratio (ρ) for each game is the quotient of the
corresponding power indexes for each team (larger divided by the
smaller). It is intended to be an indication of "pick confidence":
ρ values near 1.0 involve teams judged to be very close in
power, while large values indicate more of a mismatch.

Range

PickedRight

#Games

%

PV+HW

PV+VW

ρ

<1.01

5

9

55.6%

2

3

1.01<=

ρ

<1.05

26

41

63.4%

9

8

1.05<=

ρ

<1.10

29

46

63.0%

11

15

1.10<=

ρ

<1.15

21

41

51.2%

9

10

1.15<=

ρ

<1.20

24

32

75.0%

5

10

1.20<=

ρ

<1.30

21

28

75.0%

5

8

1.30<=

ρ

<1.50

24

29

82.8%

3

11

1.50<=

ρ

9

13

69.2%

2

4

"PV+HW" stands for "Picked Visitor and Home Won", and indicates the
number of games in each range where APR incorrectly picked the
visitor to win (and could be picked up by giving home teams more power).

"PV+VW" stands for "Picked Visitor and Visitor Won", and
indicates the number of games in each range where APR correctly
picked the visitor to win (and could be lost by giving home teams
more power).

This indicates that simply giving home teams more power would
cost more correctly picked games (where the visiting team wins)
than it would gain.

The drop off of accuracy for ρ >= 1.50 is due to the fact
that very large values of ρ are only seen at the very
beginning of the season, when APR only has a few games to produce
power indexes.